LANCASTER — Traffic was detoured from Route 70 Wednesday afternoon after a truck towing a backhoe accidentally pulled down utility poles, blocking the roadway and knocking out electricity to the neighborhood.

Officials said the driver was backing out of a driveway on Route 70 when the backhoe snagged a guy wire. The driver, not realizing the wire was hooked onto the backhoe, put the truck in drive and accelerated north on Route 70, pulling down utility poles.

One of the falling poles smashed into the passenger side of the windshield of a van. It was not immediately known whether anyone was injured.

Jackie Barry, National Grid spokeswoman, said three utility poles and all the wiring were knocked out by the accident. Initially, 800 National Grid customers, primarily in Lancaster and some in Bolton, were without power, but crews reduced those numbers to 94 by early tonight, Ms. Barry said.

"It's very extensive damage," she said, adding the repairs may go through the night or early morning.

State and local police blocked off Route 70 at Route 117, rerouting traffic through Lancaster.